1. Field of the Invention
The present invention relates to a frequency hopping modulation in a communication system, and more particularly to a method for coding a frequency hopping spread signal by modulating the frequency hopping spread signal to a chirp pulse in a wireless communication system in which a Frequency Hopping Spread Spectrum (FHSS) scheme is used.
2. Description of the Related Art
In general, a spread spectrum technology refers to a technology of transmitting specific information through the use of a much wider bandwidth than a theoretical bandwidth required for transmitting the specific information. For example, when it is assumed that there is an information source to be transmitted at a data transfer rate of 5 kbps, usually, the information source can be transmitted with a bandwidth of 5 kHz. However, when a much wider frequency bandwidth, e.g. 1 MHz, is used to transmit the information source, an error rate or signal-to-noise (S/N) ratio is enhanced although the use efficiency of the frequency band is degraded. Also, when a much wider frequency bandwidth than necessary is used, although the intensity of a spread and transmitted signal is very weak, it is possible to achieve communication, and although lots of transmitters transmit specific signals to a specific receiver at the same time, the specific signals can be delivered to the specific receiver having a specific code because the much wider frequency bandwidth provides a robust environment to minimize noise signals. That is, since one channel can be used by a plurality of users at the same time, the capacity increases proportionately.
Such a spread spectrum technology includes a direct sequence scheme, a frequency hopping scheme, a time hopping scheme, a chirp spread spectrum scheme, etc. In particular, the frequency hopping scheme is a spread spectrum scheme in which a transmission frequency is not fixed and varies according to time in a wireless communication system. That is, the frequency hopping scheme is a scheme in which a transmitting side and a receiving side communicate with each other while varying frequencies. A representative technology, to which the frequency hopping scheme is applied, is a Bluetooth technology, which is a wireless personal area network (WPAN) technology. The Bluetooth technology uses an Industrial Scientific Medical (ISM) band of 2.4 GHz, and reduces interference with other wireless communication technologies. In addition, the Bluetooth technology uses an adaptive frequency hopping scheme from version 1.5 of the Bluetooth software so as to adaptively select a channel having a low interference level at 2.4 GHz band, thereby avoids more interference.
FIG. 1 is a block diagram illustrating the configuration of a conventional frequency hopping system.
The frequency hopping system includes a frequency synthesizer 101, a frequency table 103, and a pseudo noise (PN) code generator 105. The PN code generator 105 generates PN codes relating to frequency hopping patterns, and stores the generated PN codes in the frequency table 103. The number of frequency hopping patterns stored in the frequency table 103 may vary depending on wireless communication schemes. The frequency synthesizer 101 generates a hopping frequency through the use of a frequency hopping pattern stored in the frequency table 103. Different frequency hopping spread signals may be generated depending on frequency hopping patterns stored in the frequency table 103, and a frequency hopping pattern to be used is predetermined upon a first communication channel being established. The hopping frequency generated in such a scheme is multiplied by the original signal so that a frequency hopping spread signal is produced.
FIG. 2 is a graph illustrating a frequency hopping spread signal generated by the conventional frequency hopping scheme. According to the frequency hopping spread scheme, data is transmitted using a frequency, which is not fixed and varies over time. Accordingly, since the value of the frequency varies depending on time, the number of the patterns is diversified, which means that many users can access the wireless communication at the same time.
According to such a frequency hopping scheme, when a receiving side receives data transmitted from a transmitting side, the receiving side demodulates data, which has been modulated in a predetermined hopping pattern, wherein the number of hopping patterns equates to the number of users who can simultaneously have access without interference. As the number of hopping patterns increases, more users can perform short-range wireless communication without risk of collision with other users in the same space. However, the frequency hopping scheme used in a common use frequency band, such as the ISM band, is still limited in the number of frequency hopping patterns, so that a considerable reduction of interference between users has not been achieved until the present invention. Therefore, it is necessary to develop a method which enables wireless communication to be provided to more users at the same time than the conventional frequency hopping spread spectrum scheme while reducing interference with other users, i.e. interference with other wireless communication signals.